This application makes reference to, incorporates the same herein, and claims all benefits under 35 U.S.C. xc2xa7 119 from an application entitled Paper Pickup Apparatus for a printer earlier filed in the Korean Industrial Property Office, on 31 th day of May 2000, and there duly assigned Ser. No. 2000-29596, a copy of which is annexed hereto.
1. Field of the Invention
The present invention relates to a paper pickup apparatus for a printer, and more particularly, to a paper pickup apparatus for a printer for picking up print sheets one by one from a stack on a cassette.
2. Description of Related Art
A printer for printing text and graphic images on print media such as print sheets includes a cassette on which the print sheets are stacked, a print sheet feed device for feeding a print sheet into a printing portion of the printer where a printing operation is performed, a pickup apparatus for picking up a print sheet from a stack on the cassette and transferring the print sheet to the print sheet feed device. A conventional pickup apparatus disposed adjacent to the cassette on which the print sheets are stacked includes a pickup roller for picking up print sheets one by one from the stack on the cassette and a drive motor for driving the pickup roller. The paper pickup apparatus should pick up one print sheet at a time from the stack of the cassette. In order to pick up one print sheet at a time from the cassette, the pickup roller is press-contacted with the stack by applying a predetermined press-contact force against a print sheet and then is rotated. If a press-contact force against a print sheet is very high, a plurality of print sheets may be picked up at once. On the other hand, if a press-contact force against a print sheet is very low, even one print sheet may not be picked up.
As an example to effectively pick up paper sheets one by one from the cassette, an additional plate is arranged between a bottom surface of the cassette and the stack of print sheets, and a spring is disposed between the plate and the bottom surface of the cassette, whereby the plate has an elastic force while the spring is biased to push the plate against the stack of the print sheets. As another example, a pickup roller press-contacts the stack and picks up a print sheet by pivotally moving a paper pickup apparatus using a motor toward the stack. Since a direction in which a pickup roller picks up a print sheet is opposite to a pivoting direction of the paper pickup apparatus, as the number of the print sheet stacked in the cassette varies, or as a thickness of print sheets stacked in the cassette varies, a repulsive force against a pivoting direction of the paper pickup apparatus varies and becomes greater. Due to such a repulsive force, a motor becomes overloaded, whereby durability of the motor may be reduced.
In efforts to overcome the problems described above, Optra S1650 model available from Lexmark International Inc. includes a high-capacity motor. However, as capacity of the motor becomes increased, a production cost of the motor and the printer becomes higher, and electric power is consumed more as well. U.S. Pat. No. 5,377,969 for Method and Device for Separating Sheet-Type Recording Media issued to Steinhilber discloses a paper pickup apparatus disposed to move toward direction in which a repulsive force occurs against the paper pickup apparatus. However, very complicated configurations are required to the mechanism of the paper pickup apparatus so as to move the pickup apparatus itself within the printer.
For the foregoing reasons, there is a need for a paper pickup apparatus of a printer capable of effectively picking up one paper sheet at a time from a cassette by reducing a repulsive force exerted to the paper pickup apparatus and occurred against a pivoting direction thereof.
It is an object of the present invention to provide a method and an apparatus for reducing a production cost of a paper pick-up apparatus in a printer.
It is another object to provide a method and an apparatus able to increase durability of a motor used in a paper pickup apparatus in a printer.
It is still object to provide a method and an apparatus capable of maintaining an elastic force exerted on a stack of a cassette in a printer.
It is yet another object to provide a paper pickup apparatus in a printer able to reduce a repulsive force against a pivoting direction thereof due to portion of the paper pickup apparatus rotating toward on opposite direction to the pivoting direction.
It is further object to provide a paper pickup apparatus in a printer able to prevent an overload of a motor rotating a pickup roller of the paper pickup apparatus.
It is also object to provide a method and an apparatus able to provide more space for print sheets stacked in a cassette and reduce a paper pickup apparatus and a cassette in size.
These and other objects may be achieved by using a printer to provide a paper pickup apparatus having a motor for rotating a pickup roller of a pickup roller unit and providing torque to the picup roller unit, a driving shaft rotated by the motor, a first pickup housing having at least one first transmission gear and first and second end portions, the first end portion mounted to the driving shaft, the first transmsion gear transmitting torque from the driving shaft to the second end portion, a second pickup housing having at least one second transmitting gear and rotatably mounted to the second end portion of the first pickup housing, the second transmission gear transmitting torque from the first pickup housing to the second pickup housing, a connecting portion connected between the first and second pickup housings, the first pickup housing rotatably connected to the second pickup housing centering thereon, and a pickup roller mounted to the second pickup housing and rotated by torque transmitted from the second transmission gear.
The connecting portion includes an elastic member for providing the second pickup housing unit with an elastic force toward an opposite direction to a direction that the second pickup housing rotates by a repulsive force about the first pickup housing. The elastic member is a torsion spring having first and second end portions and a central portion formed between the first and second end portions. The first end portion of the torsion is supported by the first pickup housing while the second end portion of the torsion is supported by the second pickup housing, and the central portion of the torsion is inserted around a connection shaft protruding from the second pickup housing. The first pickup housing has a first protruding portion located at a location corresponding to the first end portion of the torsion spring, and the second pickup housing has a second protruding portion located at a location corresponding to the second end portion of the torsion spring. The first pickup housing further include a limiting shaft protruding from the first pickup housing, and the second pickup housing further includes a third protruding portion extending in a longitudinal direction to contact the limiting shaft, whereby a movement that the second pickup housing rotates in the direction is limited while a reverse movement that the second pickup housing rotates the opposite direction is allowed.